Generally, semiconductor device fabrication processes which form a lamination structure of an integrated circuit on surfaces of substrates such as semiconductor wafers (hereinafter, referred to as “wafers”) include a cleaning process by which undesired objects such as fine dusts or natural oxide films, are removed from the surfaces of wafers by supplying a cleaning solution such as a chemical solution to the wafers.
A single-wafer type spin cleaning apparatus which is one type of substrate processing apparatuses for use in the aforementioned cleaning process employs a nozzle for spraying a solution, for example, an alkaline solution or an acid cleaning solution to the surface of the spinning wafer, to thereby remove the dusts or natural oxides from the surface of the wafer. In such a case, the residual liquid (cleaning solution) remaining on the surface of the wafer may be removed by rinsing the wafer with deionized water (DIW), and a subsequent wafer rotating stage for scattering and drying the wafer.
However, with the trends of high integration of semiconductor devices, so-called a pattern collapse is becoming a problem in the process of removing the aforementioned liquid from the surface of the wafer. The pattern collapse is, for example, a phenomenon where the convex portion of a convex-concave shape that forms the pattern is collapsed toward a side where more liquid remains when the balance of the surface tension for laterally extending the convex portion is broken. This phenomenon may happen when the liquid remaining at both-sides of the convex portion is not uniformly dried during the liquid removing stage of the wafer.
There is a known drying method that uses a liquid having a supercritical phase (supercritical fluid), as a method for removing the liquid from the surface of the wafer while suppressing the above-described pattern collapse phenomenon. The supercritical fluid has a relatively low viscosity as compared to a liquid and superior liquid dissolving capability having no liquid-gas interface. Therefore, the liquid on the wafer may be dried without being influenced by a surface tension by contacting and dissolving the liquid on the surface of the wafer with the supercritical fluid.
Japanese Patent Laid-Open No. 2008-72118 discloses a technique in which the substrate cleaned by a cleaning unit is conveyed into a drying apparatus by a substrate transport robot, and subsequently, brought into contact with the supercritical fluid in the drying apparatus to remove the cleaning solution from the surface of the substrate. See, for example, paragraphs [0029]˜[0033] and [0042] along with FIGS. 1, 6, 7 of Japanese Patent Laid-Open No. 2008-72118. As the cleaning unit and the drying apparatus are arranged separately from each other in the technique disclosed in Japanese Patent Laid-Open No. 2008-72118, an operation for conveying substrates between the cleaning unit and the drying apparatus is necessary, which may sacrifice an overall throughput of the substrate processing system equipped with the cleaning unit and the drying apparatus. Moreover, in a case where the cleaning solution evaporates during the substrate conveying operation, there is a possibility that a pattern collapse may occur prior to the introduction of the substrate into the drying apparatus.